JP2000316199A - Howling preventing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To sufficiently prevent howling in a room having plural frequency characteristics, and to sharply reduce the processing time. SOLUTION: At first, a CPU 40 sets PEQ 313-31n in through states, and switches a selector 22 to an A side, and allows a speaker 26 to output a white noise, and measures frequency characteristics. Then, the CPU 40 successively decides each frequency characteristics of the PFQ 311-PEQ 31n by simulation. In this case, the frequency characteristics of the PEQ 311 are decided, and then the simulation for reflecting the frequency characteristics on overall frequency characteristics is executed, and the frequencies having the maximum value are specified based on the simulated result, and the frequency characteristics of the PEQ 312 are decided for making the peak characteristics flat. Afterwards, the similar operation is repeated so that the frequency characteristics until the PEQ 31n can be set.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a howling prevention device capable of effectively preventing howling even when a room used is small.

[0002]

2. Description of the Related Art In a system in which a microphone and a speaker are used at the same time, a howling occurs when sound from the speaker goes around the microphone, and it is necessary to incorporate a howling prevention device for preventing the howling.

FIG. 3 shows a configuration of a well-known howling prevention device 1. As shown in FIG. In FIG. 1, reference numeral 10 denotes a signal generation circuit that generates white noise that is uniform in frequency.
11 is a speaker and 12 is a microphone. 13 _{1 to} 13 _n are BPFs (bandpass filters), and their center frequencies are set to be different from each other. 1
4 ₁ to 14 _n are each a peak-and-hold circuit, and outputs the peak value of the rectified corresponding BPF output signal. 15 is a selector, which is a peak and hold circuit 14
The outputs of _{1 to} 14 _n are sequentially switched and supplied to the A / D converter 16. The CPU 17 controls switching of the selector 15 and measures a peak value converted into a digital signal by the A / D converter 16.

In such a howling apparatus, the speaker 11
, A frequency-uniform white noise is generated and collected by the microphone 12. At this time, the speaker 11
Some microphones propagate directly to the microphone 12, while others propagate indirectly by being reflected on a wall or the like of a room to be used. CPU17 is sequentially switched selector 15 measures the peak output from the BPF 13 ₁ to 13 _n, detects a BPF whose output is high. Then, howling is suppressed by inserting an equalizer circuit for lowering the gain in the frequency band of the BPF in series with the microphone input.

[0005] The number of bands in which equalizing is performed in the above-described conventional howling prevention apparatus is about 5 to 9 mainly because of hardware that is limited by installation space and the like. In this case, if the frequency at which howling occurs does not match any of the center frequencies of the BPFs 13 _{1 to} 13 _n , there arises a problem that the howling cannot be sufficiently prevented.

[0006] As described above, the propagation from the speaker 11 to the microphone 12 may be direct or indirect. In particular, when the room to be used is small, the rate of indirect propagation is not negligible, and as a result of multiple reflections and interference, the frequency characteristics of the room to be used tend to be complicated to have multiple peaks. is there. In such a case, even if the above-described conventional device is used, the improvement is achieved only in one band, and howling cannot be sufficiently prevented. Recently, so-called karaoke is exploding, and there are many opportunities to use speakers and microphones even in a small room. Including this, there is an extremely high demand to prevent howling in a room having complicated frequency characteristics.

Therefore, the present applicant has proposed a howling prevention device which has solved the above-mentioned problem and has received a patent (Japanese Patent No. 27773656). This howling prevention device,
It includes a noise generator that generates white noise, a speaker that emits white noise, first to n-th equalizers that give an arbitrary frequency characteristic to the output of the microphone, and a band-pass filter that can change the center frequency. . In such a configuration, first, the first to n-th equalizers are set in a through state, and while moving the center frequency of the band-pass filter, a loop gain including a loop from the speaker to the microphone is measured, and the maximum level is measured. Is detected. Next, the first equalizer is coarsely adjusted to suppress this maximum level of frequency. Thereafter, the frequency at which the loop gain reaches the maximum level in the setting state in which the peak characteristic is suppressed is measured again, and the frequency characteristic of the first equalizer is finely adjusted. That is, by actually measuring the frequency characteristics twice,
A frequency characteristic of the first equalizer is determined. After this,
Rough adjustment and fine adjustment are performed for the second equalizer,
After that, the same operation is sequentially performed up to the n-th equalizer. Thus, howling can be prevented even when the frequency characteristic of the room to be used has a plurality of peaks.

[0008]

By the way, in the above-described howling preventing apparatus, in order to set the frequency characteristics for the first to n-th equalizers, it is necessary to perform the loop gain measurement 2n times. For this reason, the first to first
There is a problem that it takes a long time to set a desired frequency characteristic to the n-th equalizer. In addition, since white noise is emitted from the speaker during the period in which the frequency characteristic is actually measured, the user of the howling prevention device is uncomfortable.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a howling prevention apparatus capable of greatly reducing a time required to set a desired frequency characteristic. is there.

[0010]

According to the first aspect of the present invention, there is provided a sound collecting means for picking up a generated sound, and a sound picked up by the sound collecting means. In a howling prevention apparatus for preventing howling when using sounding means for amplifying and generating sound, a first to n-th equalizers for giving an arbitrary frequency characteristic to an output of the sound collecting means are connected in multiple stages. Equalizing means and, while supplying a predetermined signal to the sound generating means to generate sound, measure a signal collected by the sound collecting means to measure a frequency characteristic from the sound generating means to the sound collecting means. A frequency characteristic measuring means and a total from the sound generating means to the equalizing means based on the frequency characteristics of the first to n-th equalizers assumed as the measurement results of the frequency characteristic measuring means. Simulating means for simulating the frequency characteristic by calculation, detecting means for detecting a frequency at which the gain of the overall frequency characteristic is maximum, based on a simulation result of the simulating means, Based on the frequency, the first
Setting means for sequentially setting the frequency characteristics of the first to n-th equalizers. Further, in the invention according to claim 2, the setting means detects the frequency characteristics of the first to n-th equalizers based on a simulation result assuming that the frequency characteristics are flat by the detecting means. The frequency characteristics of the first equalizer are set so as to suppress the vicinity of the set frequency, and the frequency vicinity detected by the detection unit is suppressed based on the simulation result reflecting the setting state. So that the second
The frequency characteristic of the equalizer is set, and thereafter, this operation is repeated to set the frequency characteristic up to the n-th equalizer.

Further, in the invention according to claim 3,
The frequency characteristic measuring means measures a signal through a cascade connection of a band-pass filter having a variable center frequency and at least one or more low-pass filters having a cutoff frequency having a predetermined relationship with the center frequency. And

Further, in the invention according to claim 4,
The setting means detects an average level in a predetermined frequency range, and sets an attenuation amount in each of the first to n-th equalizers so that a level of a frequency at which a loop gain is maximum becomes the average level. It is characterized by doing.

Further, in the invention according to claim 5,
The setting unit has a storage unit that stores in advance a relationship between the Q value and the attenuation amount as a table, reads out the Q value for the attenuation amount, and sets the frequency characteristics at the time of suppression to the first to n-th. It is characterized in that it is set for each of the equalizers.

[0014] In the invention according to claim 6,
Adjusting means for adjusting a sounding level by the sounding means;
Amplifying means for variably amplifying the signal collected by the sound collecting means, wherein the setting means sets the adjusting means so as to reduce the sounding level during the setting, while the amplifying means The gain is set to be large.

According to the first aspect of the present invention, a loop gain including from the sound generating means to the sound collecting means is actually measured. Then, the first to fourth frequencies assumed to be the actually measured frequency characteristics
Based on the frequency characteristics of the n-th equalizer, the overall frequency characteristics will be simulated. Then, based on the simulation result, the frequency characteristic of each equalizer is set such that the peak of the total frequency characteristic becomes flat. Therefore, the actual measurement of the frequency measurement is performed only once,
Thereafter, the frequency characteristic of each equalizer is determined by simulation, so that the processing time can be greatly reduced.

According to the second aspect of the present invention, first, the first equalizer is set so as to suppress the frequency of the maximum level, and then, in this suppressed setting state, the loop gain is set to the maximum level. Is simulated. Then, the second equalizer is set so as to suppress the frequency having the maximum level at this time. A similar operation is set up to the n-th equalizer, so that howling can be prevented even when there are a plurality of peaks in the frequency characteristic. Further, in this case, the actual measurement of the frequency measurement is performed only once, and thereafter, the frequency characteristics of each equalizer are determined by simulation, so that the processing time can be greatly reduced.

According to the third aspect of the present invention, by measuring a signal through a cascade connection of a band-pass filter and at least one or more low-pass filters,
The cutoff characteristics of these filter outputs are improved on the high frequency side. For this reason, it is possible to more accurately measure the loop gain at a low frequency.

According to the fourth aspect of the present invention, equalization is performed by adjusting the peak level of the loop gain to the average level in a predetermined frequency range, so that not only howling is prevented but also the frequency characteristic is improved. It can be made flatter.

According to the fifth aspect of the present invention, the Q value of the frequency characteristic set for the first to n-th equalizers is set according to the amount of attenuation, so that howling is simply prevented. Instead, the frequency characteristics at that time can be made flatter.

According to the sixth aspect of the present invention, when a predetermined signal is generated by the sound generation means, the sound generation level is suppressed to a low level. Therefore, the measurer does not feel uncomfortable.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS <1. Configuration of Embodiment> An embodiment of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram showing a configuration of a howling prevention device 2 according to this embodiment.

In this figure, 21 is a signal generating circuit for generating white noise as a digital signal, 22 is a selector, 23 is a D / A converter, 24 is a volume for adjusting the output level, 25 is an amplifier, and 26 is a speaker. is there. This sound is picked up by the microphone 27. 28 is an amplifier, 29 is an A / D converter, and 30 is a variable gain amplifier. 31 _{1 to} 31 _n are parametric equalizers (PEQs) connected in cascade with each other, and the gain and frequency characteristics of the input signals are controlled by the CPU 40.

Reference numeral 32 denotes a BPF, and reference numerals 33 _{1 to} 33 _k denote low-pass filters (LPFs). These filters are
Are connected cascade to each other, LPF 33 ₁ to 3
The cutoff frequency f _C of 3 _k is set to be, for example, twice the center frequency f _{O of the} BPF 32.
As a result, BPF 32 band characteristics, LPF 33 ₁ ~ 33 _k
While the unaffected, the high-frequency side slope BPF32 output is adapted to be brought rapidly attenuated by blocking over multistage LPF 33 ₁ ~ 33 _k. In addition, BPF
32 center frequency f _O and LPF 33 ₁ ~ 33 _k cut-off frequency f _C of the while maintaining the above relationship to one another, C
It changes continuously under the control of the PU 40.

32 is a peak program meter (PPM)
The peak level of the LPF 33 _k located at the last stage is detected, and the detection result is supplied to the CPU 40. Thereby, the CPU 40 can obtain the loop gain corresponding to the frequency f ₀ at that time from the output level of the signal generation circuit 21, the setting of the volume control 24, the gain of the variable gain amplifier 30, and the output of the PPM 32.

<2. Operation of Embodiment> Next, the operation of this embodiment will be described with reference to FIG.

(Measurement of Frequency Characteristics) First, the CPU 4
0 measures the entire frequency characteristic including the transfer characteristic from the speaker 26 to the microphone 27 (step S
1). First, the CPU 40 sets each of the PEQs 31 _{1 to} 31 _n to a through state, that is, a state in which the input signal is output as it is, and switches the selector 22 to the A side so that the speaker 26 emits white noise. As a result, the microphone 27 inputs a sound to which the propagation characteristic between the microphone 27 and the speaker 24 is given and outputs the signal.

The CPU 40 includes a BPF 32 and an LPF 3
3 ₁ output signal of the microphone 27 through the ~ 33 _k was measured to determine the loop gain for the center frequency, which is initially set to BPF32 at that time. On this occasion,
The CPU 40 sets the gain of the volume 24 and the gain variable amplifier 30 as follows so that the output signal of the microphone 27 sufficiently includes a change in white noise. That is, the CPU 40 sets the gain of the variable gain amplifier 30 large while setting the gain of the volume 24 small during measurement.

As a result, the level of the measurement signal is kept low in the room at the time of measurement, so that the measurer is less likely to feel uncomfortable. Further, at the time of measurement, a large-level signal is not suddenly input to a loudspeaker having a small allowable input such as a tweeter, so that the loudspeaker can be prevented from being destroyed.

[0029] Next, CPU 40 is a cut-off frequency f _C of the center frequency f _O and LPF 33 ₁ ~ 33 _k of BPF 32, by varying while maintaining the above relationship, BPF 32
Find the loop gain for the center frequency set in. In particular, this embodiment operates at 18-18,432 Hz.
The frequency is divided at a total of 61 points every 1/6 octave in the frequency range of, and the loop gain for each of these points is obtained, and the actual measurement result is stored.

(Simulation) Next, if the loop gain at each point is obtained, the CPU 40
Parametric equalizers PEQ31 _{1 to} PEQ3
Each frequency characteristic of 1 _n is sequentially determined by simulation.
In this case, the CPU 40 manages the number of simulations using an internal register, and stores data i indicating the number of simulations therein.
(= 0) is written (step S2).

Next, the CPU 40 executes PEQ31 ₁ -PEQ31
Perform simulated of the total frequency characteristics including the characteristics of the Q31 _n. (Step S2). Specifically, step S1
PE set in step S5 to the frequency characteristic actually measured in
A total frequency characteristic is obtained by taking into account the frequency characteristic of Q. However, in the first simulation, the frequency characteristics of any of the PEQs 31 _{1 to} 31 _n have not been set yet, so that the frequency characteristics of the PEQs 31 _{1 to} 31 _n are treated as flat. On the other hand, in the second simulation, the PEQ
31 since _one of the frequency characteristic is set to simulate the overall frequency characteristic by superimposing a frequency characteristic actually measured the frequency characteristics of PEQ31 _1. Further, in the simulation of the third time, to simulate the overall frequency characteristic by superimposing a frequency characteristic actually measured the frequency characteristics of PEQ31 ₁ and PEQ31 _2. Hereafter, the already determined P
Simulate the overall frequency characteristics while reflecting the frequency characteristics of the EQ.

(Setting of PEQ Frequency Characteristics)
U40 is based on the simulation result of step 3,
The frequency f _A at which the loop gain becomes maximum among the overall frequency characteristics is detected (step S4). Thereafter, the CPU 40
Is the frequency f _A, sets the frequency characteristic of the PEQ as the center frequency when the correction of the frequency characteristic (step S
5). Specifically, for example, to set the gain to attenuation difference between the loop gain in the average value of the loop gain of the frequency range limited to the 100~10kHz and frequency f _A, further, Q value of the attenuation characteristics Is set to PEQ corresponding to the gain. Here, the correspondence between the Q value set in the PEQ and the gain is stored in advance as a table, and the Q value corresponding to the set gain is read and set.

The setting of the frequency characteristic and the target PE
Q is performed by referring to the value of data i stored in the internal register. CPU40 sets the PEQ31 ₁ frequency characteristic when i = 0, sets the PEQ31 ₂ frequency characteristics when i = 1, hereinafter, sequentially, PEQ31 ₃ ~PEQ3
The frequency characteristics of 1 _n are set. The CPU 40 stores and manages the frequency characteristic data set in each of the PEQs 31 _{3 to} 31 _n . Thereafter, the CPU 40
The value of the data i stored in the internal register is incremented by "1" (step S6), and it is determined whether the setting has been completed for all PEQs (step S6).
7). In this determination, the CPU 40 checks whether or not the value of the data i is equal to or greater than n.
After setting the Q, the selector 22 is switched to the B side. On the other hand, if the value of the data i is less than n, the process returns to step S3, and the processes from step S3 to step S7 are repeated.

By repeating the simulation of the overall frequency characteristic and the setting of the PEQ in this manner, the PEQs 31 ₁ to 31
In the PEQ 31 _n , it is possible to make each peak of the frequency characteristic in which the howling is likely to occur close to flat. Moreover, when the frequency characteristic is set for a certain PEQ, in the next simulation, the total frequency characteristic is calculated by reflecting the frequency characteristic set for the PEQ, and the next REQ is calculated based on the simulation result. Set the frequency characteristics. Therefore, when there are a plurality of peaks in the actually measured frequency characteristic, the PE
Compared to the case _where the frequency characteristics of Q31 _{1 to} PEQ31 _n are calculated, the frequency characteristics of the entire apparatus including the room to be used can be made more flat. Also, gain and Q
By setting the values in association with each other, it is possible to reduce the influence of a standing wave or the like that can occur in a standard room.

The simulation described above is executed by the CPU 4
Since the calculation is performed by zero, the processing time can be significantly reduced as compared with the case of actual measurement. For example, assuming that it takes time T to actually measure the frequency characteristic for one time, when the frequency characteristic is actually measured for n PEQs, the processing time is n · T. On the other hand, in the above-described embodiment, the time required for the simulation is very short as compared with the actually measured time T. Therefore, the processing time can be reduced to 1 / n. In particular, since noise is emitted from the speaker 26 during the actual measurement period, when the howling prevention device 2 is used as a karaoke device, the user is uncomfortable, but the actual measurement time is short in this embodiment. Therefore, discomfort during use can be greatly reduced.

<3. Modifications> The present invention is not limited to the above-described embodiment. For example, various modifications described below are possible. (1) The correspondence between the PEQ and the frequency at which the loop gain becomes maximum does not necessarily have to be in the order as in the embodiment. Further, instead of the white noise, a pink noise, a sweep signal, or the like may be used as the test signal. Since the frequency characteristic changes according to the type of the test signal, a correction curve for correcting the frequency characteristic is stored according to the type of the test signal, and the CPU 40 stores the frequency characteristic measured according to the corresponding correction curve. Is desirably corrected.

(2) In the above embodiment, A /
Although the data is converted into digital data and processed using the D / D / A in the apparatus, it is also possible to process the analog data using a switched capacitor filter or the like.

(3) In the above embodiment, the position of the microphone 27 is fixed to one place for measurement. However, in a karaoke box or the like, a singer may sing in a duet or the like. In such a case, since the microphones 27 are used at a plurality of points, howling may not be sufficiently suppressed. In the above-described embodiment, the frequency characteristic data to be set in each of the PEQs 31 _{1 to} 31 _n is generated based on the measurement result of the first point and the simulation, and is stored. Also, the microphone 27 is moved from the first point to the second point.
By moving to a point and executing the above-described measurement and simulation of the frequency characteristic, it is possible to calculate the frequency characteristic data corresponding to the second point. In this modification, the frequency characteristic data at the first point and the frequency characteristic data at the second point are compared to generate frequency characteristic data that can suppress howling regardless of which microphone 27 is used. . Hereinafter, the operation of the modification will be described with reference to FIG.

In the initial state, PEQ31 _{1 to} PEQ31 _n
The frequency characteristic data of the PE indicates the default value, and each PE
The frequency characteristics of Q31 _{1 to} PEQ31 _n are flat. In this state, the microphone 27 is positioned at the first point, and measurement and simulation of the frequency characteristic are executed. Thus, each PEQ31 ₁ ~PEQ31 _n the frequency characteristic data SET11, SET12, ... SET1n is set. In this case, the frequency characteristic data includes, for example, a suppression gain of the equalizer and a center frequency. Since the frequency characteristic data is set in order from the peak of the loop gain, the suppression gain is larger in the order of SET11, SET12,.

Next, the user moves the microphone 27 from the first point to the second point, where the frequency characteristics are measured and simulated. Then, the frequency characteristic data SE
T21, SET22,... SET2n are obtained. The CPU 40 compares the suppression gains based on these data and SET11, SET12,... SET1n obtained at the first point. Then, sorting is performed in the descending order of the suppression gain, and n data are specified from the largest one. For example, assuming that the suppression gain corresponding to SET21 is intermediate between the suppression gain corresponding to SET11 and the suppression gain corresponding to SET12, and the suppression gain corresponding to SET22 is smaller than the suppression gain corresponding to SET1n, each PEQ31 _The frequency characteristic data to be set in _{1 to} PEQ 31 _n are, as shown in the figure, SET11, SET21, SE
T12,... SET1n-1.

As described above, the frequency characteristic data of the first point is stored, the position of the microphone 27 is moved to the second point, the frequency characteristic data is obtained again, and the two are compared, and howling occurs most. Since equalizing is performed in order from the peak frequency that is easy to perform, it is possible to effectively suppress howling at a plurality of points. In addition,
By repeating the above processing, the third point, the fourth point ...
Needless to say, howling may be suppressed.

[0042]

As described above, according to the present invention, it is possible to sufficiently prevent howling in a room having complicated frequency characteristics, and to significantly reduce the processing time for that.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment according to the present invention.

FIG. 2 is a flowchart showing the operation of the embodiment according to the present invention.

FIG. 3 is a block diagram illustrating a configuration of a conventional howling prevention device.

FIG. 4 is a diagram illustrating characteristics of a bandpass filter.

FIG. 5 is a diagram for explaining an operation of a howling prevention device according to a modification.

[Explanation of symbols]

24: adjusting means, 26: speaker (sound generating means), 2
7: microphone (sound collecting means), 30: variable gain amplifier (amplifying means), 31 _{1 to} 31 _n ... parametric equalizer (equalizing means), 32: BPF,
33... LPF, 34... Peak program meter (detection means), 40... CPU (setting means).

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Akira Nishida 10-1 Nakazawacho, Hamamatsu-shi, Shizuoka F-term in Yamaha Corporation (reference) 5D020 CC05 CE01

Claims (6)

[Claims] 1. A howling preventing device for preventing howling when using sound collecting means for collecting generated sound and sound generating means for amplifying and generating a sound collected by the sound collecting means. An equalizing means comprising a multi-stage connection of first to n-th equalizers for giving an arbitrary frequency characteristic to an output of the sound collecting means; and supplying a predetermined signal to the sound generating means for sounding.
A frequency characteristic measuring unit that measures a frequency characteristic from the sound generating unit to the sound collecting unit by measuring a signal collected by the sound collecting unit; and 1
Simulating means for simulating by calculation the overall frequency characteristics from the sounding means to the equalizer means, based on the respective frequency characteristics of the nth equalizer, and based on the simulation result of the simulating means.
Detecting means for detecting a frequency at which the gain of the overall frequency characteristic is maximum; and setting means for sequentially setting the frequency characteristics of the first to n-th equalizers based on the frequency detected by the detecting means. A howling prevention device characterized by the above-mentioned. 2. The method according to claim 1, wherein the setting unit suppresses the vicinity of the frequency detected by the detection unit based on a simulation result assuming that the frequency characteristics of the first to n-th equalizers are flat. Setting the frequency characteristic of the first equalizer, and then, based on the simulation result reflecting the setting state, suppresses the vicinity of the frequency detected by the detection means, The anti-howling apparatus according to claim 1, wherein the frequency characteristic is set and then the operation is repeated to set the frequency characteristic up to the n-th equalizer. 3. The frequency characteristic measuring means transmits a signal through a cascade connection of a band-pass filter having a variable center frequency and at least one or more low-pass filters having a cutoff frequency having a predetermined relationship with the center frequency. 2. The howling prevention device according to claim 1, wherein the measurement is performed. 4. The setting means detects an average level in a predetermined frequency range, and controls the first to n-th equalizers so that the level of the frequency at which the loop gain becomes maximum becomes the average level. 3. The howling prevention device according to claim 2, wherein the amount of attenuation is set. 5. The setting means includes a storage means for storing in advance a relationship between the Q value and the attenuation amount as a table, reads out the Q value corresponding to the attenuation amount, and sets the frequency characteristic at the time of suppression to the second value. 5. The howling prevention apparatus according to claim 4, wherein the setting is made for each of the first to n-th equalizers. 6. An adjusting means for adjusting a sounding level of the sounding means, and an amplifying means for variably amplifying a signal collected by the sound collecting means, wherein the setting means performs the setting in the setting. 2. The howling prevention apparatus according to claim 1, wherein the adjusting means is set so that the sounding level is reduced, and the gain of the amplifying means is set large.